1. Field of the Invention
The present invention relates to a rescue descender system primarily, but not exclusively for use in fall arrest or fall safety systems for personnel safety when working at height.
2. State of the Art
Fall arrest or fall safety systems are known in which personnel working at height are secured to a safety line in order to arrest a fall, should this occur. Such safety lines can comprise a self retracting lifeline which includes a safety block secured to an anchor point and a safety line which pays out as the user moves away from the safety block. A brake device engages to prevent paying out of the safety line in the event of a fall. Typically the system includes an energy absorption device arranged to absorb the energy of the fall when the line payout stops in order to arrest the fall.
Typically, in the circumstances of a fall, the user can be left suspended in mid air. In order to be rescued, the user can be hooked from above by a rescuer (if in reach and accessible), or a rescuer can descend to the individual to attach them to a rescue line. Alternatively, devices have been proposed to enable a suspended user to self instigate lowering to ground or rescue level. Such arrangements are disclosed in, for example, GB2414005 and WO2009/027619. Such systems can be referred to as self rescue devices.
GB2414005 discloses a rescue descender system comprising a casing, which incorporates a bracket for attachment to a person's body harness whereby the bracket can be releasably attached to a load element attached to a safety line and the safety line may then be attached to a secure anchorage. Various release mechanisms are disclosed including release that is initiated remotely such as by the transmission and receipt of radio signals. The receipt of radio signals may be used to initiate the activation of an actuator that can then carry out the release operation. An example given of a typical actuator is a pyrotechnic actuator (explosive squib) that is initiated electrically. When the load element is released from the bracket, elongate that is also attached to the load element is deployed at a speed controlled by a speed control means thereby controlling the descent of the person being rescued.
When a person is arrested after a fall, loads of up to 6 kN can be applied between the harness and safety line
WO2009/027 length of descent line 619 discloses methods of attaching the rescue apparatus to a harness in normal use whereby the weight of the rescue apparatus is supported at least in part by alternative means other than the rigid load elements described in GB2414005.
In both documents identified, the prior art systems described use a descent line that is payed out from the descent reel is connected to the safety line by a load element and a release means actuated to permit release of the load element to allow paying out of the descent line from the descent line reel or store. In both prior art arrangements the full load of the fall and the suspended user is passed via the release means. This results in a high force necessary to effect release of the release means. Hence in WO2009/027619 the invention utilises detonation of an explosive squib as an exemplary release means for releasing the release pin 15.